X-ray CT (Computed Tomography) systems are a system that provides imaging of the interior of a subject by scanning the subject with X-ray equipment for data acquisition, and then by processing the gathered data with a computer.
Specifically, an X-ray CT system makes X-ray exposures on the subject multiple times in different directions, detects the X-rays that have passed through the subject with an X-ray detector, and acquires multiple sets of data during the detection. The detection data gathered are A/D converted by a data acquisition system and then sent to a data-processing system. The data-processing system executes preprocessing, etc. on the detection data to form projection data. Following this process, the data-processing system executes reconstruction-processing on the projection data to form tomographic data. In addition, based on multiple sets of tomographic data, the data-processing system executes further reconstruction-processing to form a volumetric data. Volumetric data are a data set that represents a three-dimensional distribution of CT values that correspond to the three-dimensional scanned region of the subject.
The X-ray CT system enables MPR (Multi Planar Reconstruction) display by rendering the volumetric data in a given direction. MPR-processed sectional images (MPR images) include three-orthogonal-axis images and oblique images. The three-orthogonal-axis images include axial images showing sections perpendicular to the axis of the body, sagittal images showing sections dividing the subject vertically along the body axis, and coronal images showing sections dividing the subject horizontally along the body axis. The oblique images are those showing sections that are not shown in three-orthogonal-axis images. In addition, the X-ray CT system produces, by rendering the volumetric data with a parameter of arbitrary eyeline, a pseudo-three-dimensional image as a view of the three-dimensional part of the subject being looked at along the eyeline.
There is a scanning method called “CT fluoroscopy” (CTF: Computed Tomography Fluoroscopy). CT fluoroscopy is a scanning method for acquiring in real time an image of the region of interest of the subject by exposing the subject to X-ray radiation continually or intermittently. In CT fluoroscopy, the rate of detection data gathering is quickened, and the time required for reconstruction-processing is shortened for real-time image generation. CT fluoroscopy is applied for monitoring purpose, for example, in a biopsy where the positional relation between the puncture needlepoint and the living tissue to be examined is monitored or in a drainage where the position of the tube used for draining fluid is monitored. By the way, the drainage herein is a method for draining bodily fluids that have accumulated in body cavities by using, for example, a tube.
During a CT fluoroscopy, actions of scanning and of medical procedure may be performed repeatedly one after the other. For example, in a case where a biopsy is performed, while reference is being made to MPR images based on volumetric data provided in CT fluoroscopy, scanning and puncturing are performed repeatedly one after the other. Specifically, at first, the subject is set in a predetermined scanning position, and an MPR image of the subject is achieved by CT fluoroscopy. Then, the subject is moved from the scanning position to a predetermined procedural position, and there, puncturing is performed while the MPR image is being referred to. After the puncture needle has been inserted to some extent, the subject is set in the scanning position again for another session of CT fluoroscopy in order to acquire a new MPR image. After that, the subject is set in the procedural position again, and the puncturing is further advanced with reference to this new MPR image. These actions are repeated until the biopsy is complete. In some other cases, a puncturing plan is made for determining a course for insertion of a puncture needle before actual puncturing is performed. Such planning also involves scanning.